1. Field of the Invention
The present invention concerns a steel for induction hardening, more specifically, a steel which can be processed as rolled without being annealed by cutting or form rolling and is suitable for induction hardening.
2. State of the Art
Taking a drive shaft with a homokinetic joint for automobiles as an example, it is manufactured in accordance with the steps of annealing or spheroidal annealing a steel for rolling such as SAE1541 to increase the machinability thereof, processing the steel by cutting or form rolling and strengthening the surface by induction hardening.
The SAE1541 steel, however, has poor machinability as rolled, and therefore, it is difficult to process the steel without heat treatment. Thus, this steel is not a suitable material from an economical point of view.
As the automobiles are getting more light-weighted and high-powered, the drive shafts should have higher strength. On the other hand, it is demanded that annealing be eliminated to enable direct cutting of the rolled steel at the request of cost reduction. To meet the request, there was proposed a steel having a composition in which manganese content of the SAE1541 steel is reduced to improve the machinability. The steel, however, has a drawback that the induction hardenability is low and the depth of surface hardened layer fluctuates.